B model mixture adjustment.

Mark - IN.

Well-known Member
I was reading the post below about the C carb idle adjustment. Same carb as the B? Reason I ask, my B quit running a week ago minutes after changing the belt on my Woods belly mower so I could mow the lawn. Dumb luck. It was a fuel issue. Specifically a carb issue. I have it running now, and seems to be running pretty good. I took the carb off, cleaned the outside, backed the mixture screw all the way out, and it was 7.5 turns from start to out. There's a plug down near the bottom of the bowl that when I took it out and looked inside, looks like a jet. Anyway, I did not take the carb apart, but dunked it, swished it, turned upside down, lifted, drained, etc for about a half hour in carb/parts cleaner and cleaned a lot of years built up gunk out. Carb is actually clean now inside as near as I can tell, and definately outside. Then I dunked it in gasoline swished, twisted, flipped, emptied a few times to get the cleaner and any silt out. I put the mixture screw back in, 7.5 turns from start. Then for the heck of it, I ran it all the way to seat. Was .75 turn, so I backed it out .75 turn. Tractor runs, appears to run ok. I can and will play with the mixture, but my question is...is there a typical starting point on the mixture screw? .75 turn would seem a little lean to me, but maybe not on this carb, or model carb. I searched the archives, and the only two posts that I saw on the B carb basically suggested playing with the mixture. Sure, I will tune the mixture, but I'm wondering if there is a rule of thumb as a starting point on mixture for the B carb? It's running and appears to be pretty good, but I have some tuning to do.

Thanks in advance.

Mark
 
It does matter the size or make of the updraft carburetor. The idle mixture screw adjusts the air for the slow idle circuit. It is to adjust the slow idle fuel mixture to cause the engine run smooth at your desired slow idle RPM's only.
A starting point can be any place but I use one and a half to two turns. The desired RPM's are determined by the stop screw setting not the adjustment screw.
The power jet would need to be removed from behind the plug to get the passage clean from the jet thru the discharge/feeder tube.
I don't attempt to remove the power jet in your type of carburetor without boiling it in soap water. Also the screwdriver needs to be ground to fit the slot in the power jet.
 
Thanks Dick. I didn't want to hijack the thread below even though they seemed similar. And today I have most of the smell out of my hands from that cleaner and that was washing them with hot soapy water about 10 times yesterday. Suppose I should have worn rubber gloves. I don't know what chemical is in that stuff, but it work pretty good. Had rust coming out of the bowl. And I swished and contorted until nothing was coming out anymore, and then did it a few times in gasoline to rince any resedue out and off.

As far as the 1.5 to 2 times out, that's where I always started with Holleys, Carters, Quadrajets and the sort, but never tried a little updraft carb like this.

Thanks again Dick.

Mark
 
I skipped the word (not) in the above post. should have said. It does(not) matter the size or make of the updraft carburetor.
 

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